This invention relates to ball joints. Ball joints are used to connect pipe sections so that the pipe sections are free to move with respect to one another.
A ball joint consists of three major parts: a case having a concavity, a so-called "ball" (actually a frustum of a hollow sphere), which fits closely within the concavity so as to form a fluid seal, and a gland (or gland ring) that urges the ball into the concavity so as to maintain the seal. Pipes attached to the ball and case are, thus, fluidly connected but can move with respect to each other.
Ball joints find particular application in dredging operations. Typically, the pipeline running from the dredge to the dump site rides on floats so that the pipeline is above the water or is partially submerged in the water. Obviously, wave action and other forces on the pipeline require that the pipe sections be free to move. These forces plus the constant wetting, high internal pressure, and presence of abrasive material (e.g., dredged sand) result in wear of the ball joint, including the gland.
Because of high operating pressures inside the pipelines, which may be several hundred pounds per square inch, a ball in a ball joint in such a pipeline is forced away from its case and against its gland. Movement of the ball (caused by movement of the pipeline) against the inner surface of the gland in contact with the ball results in accelerated wear of the inner surface of the gland.
One attempted solution to the problem was to construct a liner for the gland by placing pieces of abrasion-resistant urethane in a circumferential groove in the inner surface of the gland. These pieces were held in place by screws so that they could not move. The pieces were forced to assume the shape of the groove (i.e., mate with the groove) when the ball compressed them against the gland.
Although it resulted in reducing the bending moment required to swivel the ball, this attempted solution suffered from many disadvantages. First, it is difficult, time-consuming, and, thus, expensive to replace such a liner. Second, the liner cannot rotate within the gland during use and thereby even out the wear on it, which would prolong the liner's life.
Also known for many years in the ball joint art is a gland configuration wherein the gland contains a circumferential passageway. During use, water is pumped into the passageway and leaves through holes in a circumferential plate that forms the circumferential side of the passageway closest to the ball. The water leaving through the holes forms a thin layer of water between the gland and the ball, thereby providing lubrication between the ball and gland. The plate itself does not move within the gland nor does it itself facilitate the movement of the ball.